Process for making hydroxy-functional acrylic resins having low residual allyl monomer content

ABSTRACT

A process for making hydroxy-functional resins based on acrylate, hydroxyalkylacrylate, and allyl monomers is disclosed. The key to the process is to add the hydroxyalkylacrylate monomer in an amount and manner effective to produce a resin that contains, without vacuum stripping, less than about 1 wt. % of residual unreacted allyl monomers. Eliminating the need to vacuum strip the allyl monomer reduces process costs and enables the synthesis of new resins. The hydroxy-functional resins are readily crosslinked with melamines, polyisocyanates, or epoxies to give thermoset polymers.

FIELD OF THE INVENTION

The invention relates to hydroxy-functional acrylic resins. Inparticular, the invention relates to a process for making relatively lowmolecular weight resins from acrylate and allyl monomers. The resins areuseful in many thermoset polymer applications, especially polyurethane,melamine, and alkyd coatings.

BACKGROUND OF THE INVENTION

Hydroxy-functional acrylic resins of relatively low molecular weight(M_(n) =about 1000 to 5000) are valuable reactive intermediates formaking high-performance coatings and other thermoset polymers. Theresins are crosslinked with melamines, polyisocyanates, epoxies, andother crosslinkers to give useful thermosets.

We recently described new hydroxy-functional acrylic resins (see U.S.Pat. Nos. 5,475,073, 5,525,693, and 5,571,884) that incorporaterecurring units from allylic alcohols or alkoxylated allylic alcoholsand ordinary acrylate monomers. The resins are useful for many commonthermoset polymers (see U.S. Pat. Nos. 5,534,598 and 5,480,943). Unlikeacrylic resins previously known, preparation of these resins does notrequire a reaction solvent or chain-transfer agent to control reactivityand molecular weight. The resins are less costly because allyl alcoholand ordinary acrylate monomers are used instead ofhydroxyalkylacrylates. In addition, the resins have exceptionally lowviscosities, which makes them valuable for high-solids, low-VOCformulations.

Despite the cost and formulating advantages of hydroxy-functionalacrylic resins derived from allyl alcohol and other allylic monomers,the resins have some drawbacks. First, the advantage of using an allylmonomer, which helps to regulate molecular weight and reactivity, isoffset somewhat by the difficulty in getting all of the allyl monomer toreact completely within a reasonable time period. Usually, an excess ofthe allyl monomer is kept in the reaction mixture throughout thepolymerization, and excess unreacted allyl monomer is removed by vacuumstripping and/or stripping with water, steam, or inert gas. The examplesof U.S. Pat. No. 5,475,073 illustrate the need for vacuum stripping toremove unreacted allyl monomers. Unfortunately, vacuum stripping adds tocycle time and multiplies utility costs. Modification of commercialreactors to accommodate vacuum stripping is often costly andimpractical. In addition, the stripped allyl monomer must be recycledand reused to make the process affordable.

The need to vacuum strip allyl monomers also limits the kinds of allylmonomers that can be used and the types of resins available. Forexample, U.S. Pat. No. 5,475,073 teaches that propoxylated allylalcohols having an average of only 1 or 2 oxypropylene units can be usedbecause higher alkoxylated allylic alcohols cannot be easily strippedfrom the polymer. Preferably, alkoxylated allyl alcohols having morethan 2 oxyalkylene units could be included because a wider variety ofhydroxy-functional acrylic resins could be made.

Another key drawback relates to resins made by the earlier process thatderive from allyl monomers containing mostly secondary hydroxyl groups,e.g., propoxylated allyl alcohol-based resins. These resins can be slowin curing, especially in applications (such as automotive refinishing)for which room-temperature curing is preferred.

In sum, an improved process for making hydroxy-functional acrylic resinsis needed. Preferably, the process would retain the benefits of theearlier allyl monomer-based acrylic resin process (U.S. Pat. No.5,571,884): low raw material cost, polymerization without solvents orchain-transfer agents, low-viscosity products. In addition, however, avaluable process would give resins that cure rapidly even at roomtemperature. Ideally, the process would eliminate the need to vacuumstrip and recycle allyl monomers, and would permit the use of higheralkoxylated allylic alcohols.

SUMMARY OF THE INVENTION

The invention is a process for making a hydroxy-functional acrylicresin. The process comprises copolymerizing, in the presence of afree-radical initiator, an acrylate monomer, an allyl monomer, and ahydroxyalkylacrylate monomer. The acrylate monomer is a C₁ -C₂₀ alkyl oraryl acrylate or methacrylate. The allyl monomer is selected fromallylic alcohols, alkoxylated allylic alcohols, allyl esters, allylcarbonates, and allyl ethers. An ethylenic monomer is optionallyincluded. The reaction product is a hydroxy-functional acrylic resinthat has a hydroxyl number within the range of about 20 to about 500 mgKOH/g. A key to the process is to add a hydroxyalkylacrylate ormethacrylate monomer in an amount and manner effective to produce aresin that contains, without vacuum stripping, less than about 1 wt. %,based on the amount of resin, of residual unreacted allyl monomers.

I surprisingly found that, in a process for making hydroxy-functionalacrylic resins from allyl monomers and ordinary acrylates, the need forvacuum stripping and recycle of allyl monomers can be overcome byperforming the polymerization in the presence of ahydroxyalkyl(meth)acrylate monomer. The hydroxyalkyl(meth)acrylatemonomer unexpectedly enables continued polymerization of the allylmonomers to very low concentrations, effectively eliminating the needfor vacuum stripping. Because vacuum stripping is not needed,alkoxylated allylic alcohols having more than 2 oxyalkylene units caneasily be incorporated into the resins. An added benefit of the processis the production of resins having primary hydroxyl group functionalityand correspondingly improved room-temperature curing properties.Moreover, the process of the invention offers these advantages, yetstill retains the benefits of our recent technology for makinghydroxy-functional acrylic resins--low cost, absence of solvents andchain-transfer agents, and low-viscosity products.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention comprises copolymerizing an acrylatemonomer, an allyl monomer, and a hydroxyalkylacrylate monomer to producea hydroxy-functional acrylic resin.

Acrylate monomers suitable for use in the process of the invention areordinary C₁ -C₂₀ alkyl or aryl acrylates or methacrylates (hereinaftercollectively called "(meth)acrylates.") Not included arehydroxy-functional acrylate monomers. Preferred monomers are C₁ -C₁₀alkyl or aryl (meth)acrylates. Examples include methyl acrylate, methylmethacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, andthe like, and mixtures thereof. It is often advantageous to use mixturesof various acrylates and methacrylates to control the resinglass-transition temperature.

An allyl monomer is included in the process of the invention. Suitableallyl monomers include allylic alcohols, alkoxylated allylic alcohols,allyl esters, allyl carbonates, and allyl ethers. Allylic alcoholsuseful in the process of the invention preferably have the generalstructure: CH₂ ═CR--CH₂ --OH in which R is selected from the groupconsisting of hydrogen and C₁ -C₅ alkyl. Suitable allylic alcoholsinclude, for example, allyl alcohol, methallyl alcohol,2-ethyl-2-propen-1-ol, and the like, and mixtures thereof. Allyl alcoholand methallyl alcohol are preferred.

Alkoxylated allylic alcohols are also suitable monomers for use in theprocess. Preferred alkoxylated allylic alcohols have the generalstructure CH₂ ═CR--CH₂ --(A)_(n) --OH in which A is an oxyalkylenegroup, R is selected from the group consisting of hydrogen and C₁ -C₅alkyl, and n, which is the average number of oxyalkylene groups in thealkoxylated allylic alcohol, has a value from 1 to 50. Preferredoxyalkylene groups are oxyethylene, oxypropylene, oxybutylenes, andmixtures thereof. Most preferred are ethoxylated and propoxylatedallylic alcohols having an average of 1 to 10 oxyalkylene groups.

Suitable alkoxylated allylic alcohols can be prepared by reacting anallylic alcohol with up to about 50 equivalents of one or more alkyleneoxides in the presence of a basic catalyst as described, for example, inU.S. Pat. Nos. 3,268,561 and 4,618,703, the teachings of which areincorporated herein by reference. As will be apparent to those skilledin the art, suitable alkoxylated allylic alcohols can also be made byacid catalysis, as described, for example, in J. Am. Chem. Soc. 71(1949) 1152.

Allyl esters can also be used in the process of the invention. Preferredallyl esters have the general structure: CH₂ ═CR--CH₂ --O--CO--R' inwhich R is selected from the group consisting of hydrogen and C₁ -C₅alkyl, and R' is hydrogen or a saturated or unsaturated linear,branched, or cyclic C₁ -C₃₀ alkyl, aryl, or aralkyl group. Suitableallyl esters include, for example, allyl formate, allyl acetate, allylbutyrate, allyl benzoate, methallyl acetate, allyl fatty esters, and thelike, and mixtures thereof. Particularly preferred are allyl estersderived from allyl alcohol and methallyl alcohol. Most preferred are C₁-C₅ alkyl esters of allyl alcohol and methallyl alcohol.

Preferred allyl carbonates have the general structure: CH₂ ═CR--CH₂--O--CO₂ R', wherein R is selected from the group consisting of hydrogenand C₁ -C₅ alkyl, and R' is a saturated linear, branched, or cyclic C₁-C₃₀ alkyl, aryl, or aralkyl group. Suitable allyl carbonates include,for example, methyl allyl carbonate, ethyl methallyl carbonate, and thelike, and mixtures thereof. Minor amounts of bis(allyl) carbonates suchas bis(allyl) carbonate can also be included.

Preferred allyl ethers have the general structure: CH₂ ═CR--CH₂ --O--R'in which R is selected from the group consisting of hydrogen and C₁ -C₅alkyl, and R' is a saturated linear, branched, or cyclic C₁ -C₃₀ alkyl,aryl, or aralkyl group. Suitable allyl ethers include, for example,allyl methyl ether, allyl ethyl ether, allyl tert-butyl ether, allylmethylbenzyl ether, and the like, and mixtures thereof.

The relative amount of C₁ -C₂₀ alkyl or aryl (meth)acrylate and allylmonomers used in the process of the invention depends on many factors,including the desired degree of hydrophilicity and hydroxyl content ofthe resin, the nature of the monomers used, suitability for a particularend-use application, and other factors. Preferably, hydroxy-functionalacrylic resins made by the process of the invention contain (based onthe amount of resin) from about 40 to about 90 wt. % of recurring unitsderived from the C₁ -C₂₀ alkyl or aryl (meth)acrylate monomer, and fromabout 5 to about 60 wt. % of recurring units derived from the allylmonomer. More preferably, the resins contain from about 50 to about 80wt. % of recurring units derived from the C₁ -C₂₀ alkyl or aryl(meth)acrylate monomer, and from about 10 to about 50 wt. % of recurringunits derived from the allyl monomer.

A hydroxyalkylacrylate or methacrylate monomer is used in the process ofthe invention. Preferred hydroxyalkyl(meth)acrylates have the generalstructure: H--(A)_(n) --O--(C═O)--CR═CH₂ wherein A is an oxyalkylenegroup (preferably oxyethylene or oxypropylene), n has a value from 1 to5 (preferably 1), and R is hydrogen or a C₁ -C₅ alkyl group.Particularly preferred hydroxyalkyl(meth)acrylates arehydroxyethylacrylate, hydroxyethylmethacrylate, hydroxypropylacrylate,hydroxypropylmethacrylate, and the like, and mixtures thereof.

The amount of hydroxyalkyl(meth)acrylate used in the process depends onmany factors, including the target hydroxyl number of the resin, thedesired primary hydroxyl group content of the resin, the nature of themonomers used, the desired hydrophilicity of the resin, and otherfactors. Preferably, the amount of hydroxyalkyl(meth)acrylate used is atleast about 5 wt. % based on the total amount of hydroxy-functionalmonomers used. (The total amount is the sum of allylic alcohol,alkoxylated allylic alcohol, and hydroxyalkyl(meth)acrylate monomersused.) Thus, the hydroxyalkyl(meth)acrylate can be the onlyhydroxy-functional monomer present (if, for example, anon-hydroxy-functional monomer such as an allyl ester or allyl ether isused as the only allyl monomer). Resins made by the process of theinvention preferably contain up to about 60 wt. %, based on the amountof resin, of hydroxy-functional monomers.

Optionally, one or more ethylenic monomers is included in thecopolymerization process of the invention. The ethylenic monomer isoften included to control resin solubility, enhance physical properties,or reduce cost. When present, the ethylenic monomer is preferably usedin an amount within the range of about 0.1 to about 50 wt. %. A morepreferred range is from about 1 to about 25 wt. %. Preferred ethylenicmonomers include, for example, vinyl aromatic monomers, unsaturatednitrites, vinyl esters, vinyl ethers, vinyl halides, vinylidene halides,unsaturated anhydrides, unsaturated dicarboxylic acids, acrylic andmethacrylic acids, acrylamide and methacrylamide, fluoroalkylacrylatesand methacrylates, conjugated dienes, and the like, and mixturesthereof. When an optional ethylenic monomer is included in the process,it is preferred to add it in proportion to the C₁ -C₂₀ alkyl or aryl(meth)acrylate monomer.

The process is performed in the presence of a free-radical initiator.Peroxide, hydroperoxide, and azo initiators well known to those skilledin the art are preferred. Preferred initiators have a decompositiontemperature greater than about 100° C. Suitable peroxide initiatorsinclude, for example, t-butylperoxide, t-butyl hydroperoxide,di-t-butylperoxide, t-butyl perbenzoate, cumene hydroperoxide, dicumylperoxide, and the like. The amount of free-radical initiator neededvaries, but it is generally within the range of about 0.1 to about 10wt. % based on the total amount of monomers used. Preferably, the amountof free-radical initiator used is within the range of about 1 to about 5wt. %. Generally, it is preferred to add the free-radical initiatorgradually during the course of the polymerization; it is also desirableto match the addition rate of the free-radical initiator to the additionrate of the C₁ -C₂₀ alkyl or aryl (meth)acrylate monomer.

Resins made by the process of the invention have hydroxyl functionality.Preferably, the resins have average hydroxyl functionalities within therange of about 2 to about 30; a more preferred range is from about 3 toabout 15. The resins preferably have hydroxyl numbers within the rangeof about 20 to about 500 mg KOH/g; a more preferred range is from about50 to about 200 mg KOH/g.

Resins made by the process of the invention preferably have numberaverage molecular weights within the range of about 500 to about 50,000;a more preferred range is from about 1000 to about 10,000; mostpreferred is the range from about 1000 to about 5000.

Glass-transition temperatures (T_(g)) of resins made by the process ofthe invention can vary over a broad range. Preferably, the resins have aT_(g) within the range of about -50° C. to about 100° C. A morepreferred range is from about -40° C. to about 60° C.

The process of the invention can be performed over a wide temperaturerange. Generally, the reaction temperature will be within the range ofabout 60° C. to about 300° C. A more preferred range is from about 90°C. to about 200° C.; most preferred is the range from about 100° C. toabout 180° C.

The process of the invention is advantageously performed in the absenceof any reaction solvent, but a solvent may be included if desired.Useful solvents are those that will not interfere with the free-radicalpolymerization reaction or otherwise react with the monomers. Suitablesolvents include ethers, esters, ketones, aromatic and aliphatichydrocarbons, alcohols, glycol ethers, glycol ether esters, and thelike, and mixtures thereof.

Preferably, at least about 50% of the C₁ -C₂₀ alkyl or aryl acrylates ormethacrylate is added gradually to the reaction mixture duringpolymerization. Gradual addition of the acrylate helps to ensure an evendistribution of hydroxyl groups in the polymer. The acrylate monomersare generally much more reactive than the allyl monomer, so an excess ofthe allyl monomer is preferably maintained in the reactor during most ofthe polymerization.

The hydroxyalkyl(meth)acrylate monomer is added in an amount and mannereffective to produce a hydroxy-functional acrylic resin that contains,without vacuum stripping, less than about 1 wt. % (based on the amountof resin) of residual unreacted allyl monomers. To achieve this result,at least some hydroxyalkyl(meth)acrylate monomer is added to thereaction mixture in the later stages of the polymerization. Preferably,enough hydroxyalkyl(meth)acrylate is added in finishing thepolymerization to maintain a weight ratio in the reactor ofhydroxyalkyl(meth)acrylate to unreacted allyl monomer within the rangeof about 2:1 to about 3:1. For example, if the reaction mixture at ornear the end of the polymerization contains about 5 wt. % of unreactedallyl monomer, it is preferred to finish the polymerization with fromabout 10 to about 15 wt. % of hydroxyalkyl(meth)acrylate.

In one preferred approach, illustrated below in Example 1, all of theallyl monomer is charged initially. Portions of the ordinary acrylatemonomer, ethylenic monomer, and free-radical initiator are chargedinitially to the reactor, while most of the rest is added gradually at adecreasing rate during polymerization. All of thehydroxyalkyl(meth)acrylate monomer is then combined with the remainingacrylate monomer, ethylenic monomer, and free-radical initiator, andthis mixture is added at a relatively constant rate to finish thepolymerization. Note: For safety reasons, the free-radical initiator ispreferably added separately in large-scale preparations.! In the absenceof the hydroxyalkyl(meth)acrylate monomer, a substantial amount (usually5-30 wt. %) of unreacted allyl monomer remains in the product (see,e.g., Comparative Example 4). I surprisingly found, however, thatfinishing the polymerization with hydroxyalkyl(meth)acrylate presentunexpectedly enables continued polymerization of the allyl monomers tovery low concentrations and effectively eliminates the need for vacuumstripping.

Example 6 illustrates another preferred approach. In this case, all ofthe allyl monomer is charged initially. A portion of the ordinaryacrylate monomer, ethylenic monomer, and free-radical initiator arecharged initially to the reactor as in Example 1, while the rest isadded gradually at a decreasing rate during polymerization. Thehydroxyalkyl(meth)acrylate monomer is coincidentally added at arelatively constant rate. Relative to the other monomers, the amount ofthe hydroxyalkyl(meth)acrylate monomer being fed to the reactorincreases as a function of time and is greatest at the end of thepolymerization.

The key is to use enough of the hydroxyalkyl(meth)acrylate monomer atthe later stages of the polymerization to achieve essentially completepolymerization of the allyl monomer(s). Exactly how muchhydroxyalkyl(meth)acrylate monomer is used and how it is introduceddepends on many factors within the control of the skilled person. Animportant consideration is the amount of allyl monomer used. When agreater proportion of allyl monomer is used, the amount ofhydroxyalkyl(meth)acrylate needed may be greater. Another factor toconsider is the desired distribution of primary hydroxyl functionalityin the resin. If an even distribution of primary hydroxyl groups isimportant, a hydroxyalkyl(meth)acrylate such as hydroxyethylacrylate mayneed to be introduced throughout the polymerization (as shown, e.g., inExample 6).

When the process of the invention is used, the amount of residualunreacted allyl monomer present at the end of the polymerization,without using any vacuum stripping, is less than about 1 wt. % based onthe amount of resin. Preferably, the amount of allyl monomer remainingis less than about 0.5 wt. % based on the amount of resin. While avacuum strip procedure can be used in combination with the process tofurther reduce the level of allyl or other monomers present, eliminatingthe need for such a vacuum strip is a distinct advantage of the processof the invention.

Elimination of vacuum stripping reduces cycle time and saves on utilitycosts. Further savings result from the process because there is no needto recycle and reuse the allyl monomer. Because the need to vacuum stripthe polymer is obviated, the process of the invention broadens theselection of possible allyl monomers and enables the synthesis of newresins based on higher alkoxylated allylic alcohols. For example,propoxylated allyl alcohols having 3-50 oxyalkylene units that could notbe made practically by earlier methods can be made with the process ofthe invention.

Another advantage of the process of the invention is the ability to makeacrylic polymers with evenly distributed hydroxyl groups. In the absenceof an allyl monomer, hydroxyalkyl(meth)acrylates tend to homopolymerizeand give polymers with unevenly distributed hydroxyl groups.Crosslinkable polymers that contain an even distribution of OH groupsare expected to give thermosets with improved physical and mechanicalproperties.

Resins made by the process of the invention can be fine-tuned to controlthe amount and distribution of primary and secondary hydroxyl end groupsin the resin. For example, by varying the proportion of propoxylatedallyl alcohol (secondary OH groups) and hydroxyethylacrylate (primary OHgroups), one can make resins that have the desired level of reactivityfor thermoset applications such as melamine or polyurethane coatings. Acoating resin that cures sluggishly at room temperature because of ahigh content of secondary hydroxyl groups may be improved, for example,by increasing the proportion of hydroxyethylacrylate in the resin (see,e.g., Example 7 and Comparative Example 8).

Resins made by the process of the invention are useful in a variety ofthermoset polymer applications. These applications normally react ahydroxy-functional resin with a crosslinker to make the thermosetpolymer. Examples include polyesters, polyurethanes, melamines, alkyds,uralkyds, and epoxies. These thermoset technologies, which are generallywell known in the art, are explained in more detail in U.S. Pat. Nos.5,534,598 and 5,480,943, the teachings of which are incorporated hereinby reference.

The following examples merely illustrate the invention. Those skilled inthe art will recognize many variations that are within the spirit of theinvention and scope of the claims.

EXAMPLE 1

Allyl alcohol monopropoxylate (138 g) is charged to a one-liter reactionkettle equipped with agitator, heating mantle, temperature controller,nitrogen purge device, condenser, and addition pump. In a separatevessel, styrene (35 g), methyl methacrylate (35 g), butyl methacrylate(241 g), butyl acrylate (49 g), and t-butylperbenzoate (20 g) are mixed,deoxygenated with nitrogen, and chilled to 5° C. A portion (50 g) ofthis mixture is charged to the reactor; the rest is charged to theaddition pump. After purging three times with nitrogen, the reactor issealed and the contents are heated to 145° C. The mixture in theaddition pump is added gradually to the polymerization reactor at adecreasing rate as follows: first hour: 100 g; second hour: 80 g; thirdhour: 65 g; fourth hour: 50 g; fifth hour: 35 g. After the fifth hour,the addition pump is charged with a mixture of styrene (17.5 g), methylmethacrylate (17.5 g), butyl methacrylate (120.5 g), butyl acrylate(24.5 g), hydroxyethylacrylate (69 g), and t-butylperbenzoate (10 g).The mixture is added to the reactor at 145° C. at a constant rate over 2h. Heating at 145° C. continues for another 0.5 h following completionof monomer addition. No vacuum stripping procedure is used. Note: Forsafety reasons, the free-radical initiator is preferably addedseparately in large-scale preparations.!

The resulting polymer (676 g) has Mw=13,400; Mn=3860; glass-transitiontemperature=-15° C.; and hydroxyl number (solid resin) 121 mg KOH/g.Content of residual monomers (wt. %): allyl alcohol monopropoxylate:0.32; hydroxyethylacrylate: 0.030; butyl acrylate: 0.030; butylmethacrylate: 0.26; styrene: 0.004; methyl methacrylate: 0.022.

EXAMPLE 2

The procedure of Example 1 is followed, with the followingmodifications: (1) the polymerization is performed at 135° C. instead of145° C.; (2) after completing the addition of the mixture ofhydroxyethylacrylate and other monomers, heating continues for 1 hinstead of 0.5 h.

The resulting polymer (697 g) has Mw=10,900; Mn=4100; glass-transitiontemperature=-17° C.; and hydroxyl number (solid resin) 126 mg KOH/g.Content of residual monomers (wt. %): allyl alcohol monopropoxylate:0.48; hydroxyethylacrylate: none detected; butyl acrylate: nonedetected; butyl methacrylate: 0.19; styrene: 0.030; methyl methacrylate:0.024.

EXAMPLE 3

The procedure of Example 1 is followed using hydroxyethylmethacrylate(69 g) instead of hydroxyethylacrylate.

The resulting polymer (680 g) has Mw =13,400; Mn=3860; glass-transitiontemperature=-15° C.; and hydroxyl number (solid resin) 119 mg KOH/g.

COMPARATIVE EXAMPLE 4

Allyl alcohol monopropoxylate (138 g) is charged to a one-liter reactionkettle equipped with agitator, heating mantle, temperature controller,nitrogen purge device, condenser, and addition pump. In a separatevessel, styrene (35 g), methyl methacrylate (35 g), butyl methacrylate(254 g), butyl acrylate (49 g), and t-butylperbenzoate (30 g) are mixed,deoxygenated with nitrogen, and chilled to 5° C. A portion (45 g) ofthis mixture is charged to the reactor; the rest is charged to theaddition pump. After purging three times with nitrogen, the reactor issealed and the contents are heated to 145° C. The mixture in theaddition pump is added gradually to the polymerization reactor at adecreasing rate as follows: first hour: 86 g; second hour: 75 g; thirdhour: 65 g; fourth hour: 48 g; fifth hour 37 g; sixth hour: 28 g;seventh hour: 19 g. Heating at 145° C. continues for another 1 hfollowing completion of monomer addition.

The polymer product is vacuum stripped at up to 160° C., and about 45 gof unreacted allyl alcohol monopropoxylate is collected. The resultingpolymer has Mw=10,520; Mn=3220; glass-transition temperature=-24° C.;and hydroxyl number (solid resin) 118 mg KOH/g.

EXAMPLE 5

Allyl alcohol monopropoxylate (138 g) is charged to a one-liter reactionkettle equipped as in Example 1. In a separate vessel, styrene (35 g),methyl methacrylate (35 g), butyl methacrylate (241 g), butyl acrylate(49 g), methacrylic acid (48 g), and t-butylperbenzoate (20 g) aremixed, deoxygenated with nitrogen, and chilled to 5° C. A portion (56 g)of this mixture is charged to the reactor; the rest is charged to theaddition pump. After purging three times with nitrogen, the reactor issealed and the contents are heated to 135° C. The mixture in theaddition pump is added gradually to the polymerization reactor at adecreasing rate as follows: first hour: 113 g; second hour: 90 g; thirdhour: 73 g; fourth hour: 56 g; fifth hour 39 g. After the fifth hour,the addition pump is charged with a mixture of styrene (10.9 g), methylmethacrylate (10.9 g), butyl methacrylate (75.4 g), butyl acrylate (15.3g), hydroxyethylacrylate (43.2 g), methacrylic acid (15 g), andt-butylperbenzoate (10 g). The mixture is added to the reactor at 135°C. at a constant rate over 2 h. Heating at 135° C. continues for another1 h following completion of monomer addition. No vacuum strippingprocedure is used.

The resulting polymer (740 g) has Mw=17,350; Mn=5530; glass-transitiontemperature=-15° C.; acid number (solid resin) 40 mg KOH/g; and hydroxylnumber (solid resin) 151 mg KOH/g. Content of residual monomers (wt. %):allyl alcohol monopropoxylate: 0.28; hydroxyethylacrylate: nonedetected; butyl acrylate: none detected; butyl methacrylate: 0.26;styrene: 0.037; methyl methacrylate: 0.067.

EXAMPLE 6

Allyl alcohol monopropoxylate (285 g), methyl amyl ketone (500 g), andt-butylperoxide (80 g) are charged to a five-liter stainless-steelreactor equipped with agitator, oil heating jacket, temperaturecontroller, nitrogen purge device, and two addition pumps. In a separatevessel, styrene (143 g), methyl methacrylate (143 g), butyl methacrylate(1064 g), and butyl acrylate (204 g) are mixed and deoxygenated withnitrogen. A portion (229 g) of this mixture is charged to the reactor;the rest is charged to the first addition pump. Hydroxyethylacrylate(285 g) is purged with nitrogen and charged to the second addition pump.After purging three times with nitrogen, the reactor is sealed and thecontents are heated to 135° C. The mixture in the first addition pump isadded gradually to the polymerization reactor at a decreasing rate asfollows: first hour: 310 g; second hour: 280 g; third hour: 250 g;fourth hour: 200 g; fifth hour: 150 g; sixth hour: 135 g. Meanwhile, thehydroxyethylacrylate is added to the mixture from the second additionpump at a constant rate of 47.5 g per hour. Heating at 135° C. continuesfor another 0.5 h following completion of monomer addition. No vacuumstripping procedure is used.

The resulting polymer has Mw=9800; Mn=4080; glass-transitiontemperature=-10° C.; and hydroxyl number (solid resin) 138 mg KOH/g.Content of residual monomers (wt. %): allyl alcohol monopropoxylate:0.10; hydroxyethylacrylate: 0.11; butyl acrylate: 0.05; butylmethacrylate: 0.06; styrene: 0.01; methyl methacrylate: 0.03.

EXAMPLE 7

The resin solution of Example 6 (15 g) is mixed with methyl amyl ketone(2 g), t-butyl acetate (2 g), LUXATE HT2090 HDI trimer (5.4 g, productof ARCO Chemical Company), and dibutyltin dilaurate (0.005 g of a 2%solution in methyl amyl ketone). The coating solution is drawn down on atest panel with a thickness of 3 mils to test dry time. A "Bi-Cycle"Drying Time Recorder is used. The coating requires 4 h to set to touch,5.5 h to dry through, and 7 h to dry hard.

COMPARATIVE EXAMPLE 8

The procedure of Example 7 is followed, except that the resin solutionis prepared according to Comparative Example 4. The coating requiresgreater than 24 h to set to touch.

The preceding examples are meant only as illustrations; the followingclaims define the scope of the invention.

I claim:
 1. A process which comprises copolymerizing a C₁ -C₂₀ alkyl oraryl(meth)acrylate monomer with one or more allyl monomers selected fromthe group consisting of allylic alcohols, alkoxylated allylic alcohols,allyl esters, allyl carbonates, and allyl ethers, optionally in thepresence of an ethylenic monomer, and in the presence of a free-radicalinitiator and a hydroxyalkyl(meth)acrylate monomer, to produce ahydroxy-functional acrylic resin having a hydroxyl number within therange of about 20 to about 500 mg KOH/g;wherein thehydroxyalkyl(meth)acrylate monomer is added in an amount and mannereffective to produce a hydroxy-functional acrylic resin that contains,without vacuum stripping, less than about 1 wt. %, based on the amountof resin, of residual unreacted allyl monomers.
 2. The process of claim1 wherein the C₁ -C₂₀ alkyl or aryl(meth)acrylate monomer is selectedfrom the group consisting of C₁ -C₁₀ alkyl(meth)acrylates.
 3. Theprocess of claim 1 wherein the allyl monomer is allyl alcohol.
 4. Theprocess of claim 1 wherein the allyl monomer is an alkoxylated allylicalcohol of the formula: CH₂ ═CR--CH₂ --(A)_(n) --OH in which A is anoxyalkylene group, R is hydrogen or a C₁ -C₅ alkyl group, and n, whichis the average number of oxyalkylene groups, has a value within therange of about 1 to about
 50. 5. The process of claim 1 wherein theethylenic monomer is one or more monomers selected from the groupconsisting of vinyl aromatic monomers, unsaturated nitriles, vinylesters, vinyl ethers, vinyl halides, vinylidene halides, unsaturatedanhydrides, unsaturated dicarboxylic acids, acrylic and methacrylicacids, acrylamide and methacrylamide, fluoroalkylacrylates andmethacrylates, and conjugated dienes.
 6. The process of claim 1 whereinthe hydroxyalkyl(meth)acrylate monomer is selected from the groupconsisting of hydroxyethylacrylate, hydroxyethylmethacrylate,hydroxypropylacrylate, hydroxypropylmethacrylate, and mixtures thereof.7. The process of claim 1 wherein the hydroxy-functional acrylic resinhas a hydroxyl number within the range of about 50 to about 200 mgKOH/g.
 8. The process of claim 1 wherein at least about 50 wt. % of theC₁ -C₂₀ alkyl or aryl(meth)acrylate monomer is added gradually to thereaction mixture during polymerization.
 9. The process of claim 1wherein the hydroxy-functional acrylic resin contains from about 40 toabout 90 wt. % of recurring units derived from the C₁ -C₂₀ alkyl oraryl(meth)acrylate monomer, from about 5 to about 60 wt. % of recurringunits derived from the allyl monomer, both amounts based on the amountof hydroxy-functional acrylic resin, and at least about 5 wt. %, basedon the total amount hydroxy-functional monomers used, of thehydroxyalkyl(meth)acrylate monomer.
 10. The process of claim 1 whereinthe hydroxy-functional acrylic resin has a number average molecularweight within the range of about 500 to about 50,000.
 11. A processwhich comprises:(a) charging a reactor with an allyl monomer selectedfrom the group consisting of allylic alcohols, alkoxylated allylicalcohols, allyl esters, allyl carbonates, and allyl ethers; (b)gradually adding to the reactor, at a decreasing rate, major portions ofa free-radical initiator, a C₁ -C₂₀ alkyl or aryl(meth)acrylate monomer,and optionally, an ethylenic monomer while heating the reactor contentsat a temperature within the range of about 60° C. to about 300° C. tocopolymerize the monomers; and (c) finishing the polymerization byadding to the reactor a hydroxyalkyl(meth)acrylate monomer and theremaining minor portions of free-radical initiator, C₁ -C₂₀ alkyl oraryl(meth)acrylate monomer, and optional ethylenic monomer, wherein thehydroxyalkyl(meth)acrylate monomer is used in an amount and mannereffective to produce a hydroxy-functional acrylic resin that contains,without vacuum stripping, less than about 1 wt. %, based on the amountof resin, of residual unreacted allyl monomers.
 12. The process of claim11 wherein the C₁ -C₂₀ alkyl or aryl(meth)acrylate monomer is selectedfrom the group consisting of C₁ -C₁₀ alkyl(meth)acrylates.
 13. Theprocess of claim 11 wherein the allyl monomer is allyl alcohol or analkoxylated allylic alcohol of the formula: CH₂ ═CR--CH₂ --(A)_(n) --OHin which A is an oxyalkylene group, R is hydrogen or a C₁ -C₅ alkylgroup, and n, which is the average number of oxyalkylene groups, has avalue within the range of about 1 to about
 50. 14. The process of claim11 wherein the ethylenic monomer is one or more monomers selected fromthe group consisting of vinyl aromatic monomers, unsaturated nitriles,vinyl esters, vinyl ethers, vinyl halides, vinylidene halides,unsaturated anhydrides, unsaturated dicarboxylic acids, acrylic andmethacrylic acids, acrylamide and methacrylamide, fluoroalkylacrylatesand methacrylates, and conjugated dienes.
 15. The process of claim 11wherein the hydroxy-functional acrylic resin has a hydroxyl numberwithin the range of about 20 to about 500 mg KOH/g.
 16. The process ofclaim 11 wherein the hydroxy-functional acrylic resin contains fromabout 40 to about 90 wt. % of recurring units derived from the C₁ -C₂₀alkyl or aryl(meth)acrylate monomer, from about 5 to about 60 wt. % ofrecurring units derived from the allyl monomer, both amounts based onthe amount of hydroxy-functional acrylic resin, and at least about 5 wt.%, based on the total amount hydroxy-functional monomers used, of thehydroxyalkyl(meth)acrylate monomer.